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Body Logistics > 5. Glands Introduction > Flashcards

5. Glands Introduction Flashcards

1
Q

What is a gland?

A

An epithelial cell or an aggregate of epithelial cells that are specialised for the secretion of a substance

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2
Q

What is secretion?

A

The production and release of materials by a cell or aggregate of cells

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3
Q

How are glands classified?

A

According to their structure and how their products are released

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4
Q

What are the two types of glands?

A

Endocrine and exocrine

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5
Q

What is the difference between endocrine and exocrine?

A

Endocrine is ductless - secrete directly into blood flowing through them, secretions are hormones.
Exocrine are ducted - these secrete into a location or region of the body through a duct, secretions are mostly enzymes or lubricants.

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6
Q

What are some examples of endocrine glands?

A

The pituitary gland, thyroid gland, parathyroid gland

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7
Q

What is released from the anterior pituitary?

A

ACTH, LH, FSH, TSH regulating glands
Prolactin stimulates milk production
Somatotrophin growth of body and tissues

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8
Q

What is released from the posterior pituitary?

A

Vasopressin (ADH) - prevents water loss from kidneys

Oxytocin - delivery, ejection of milk

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9
Q

What is released from the thyroid and parathyroid?

A

Thryoid - thyroid hormones T3 and T4, calcitonin

Parathyroid - PTH, calcium homeostasis

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10
Q

What are some examples of exocrine secretions?

A

Salivary glands - saliva
Pancreas - secretes enzymes, amylase, trypsin, lipase.
Mammary - colostrum and milk
Sweat glands - sweat
Sebaceous gland - sebum onto skin and ear
Lachrymal - water to moisten eye, lysozyme for bacteria.

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11
Q

Describe the histology of the two types of glands.

A

Endocrine contains hormone-producing epithelial cells, stores precursor of hormone, blood vessel local.
Exocrine contains two layers of cuboidal cells - compound epithelial cells.

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12
Q

How do glands develop?

A
  1. 4 weeks gestation, growth signal received from fibroblast growth factor family member
    Mesenchymal cells, produce e.g. FGF10 FGF8/7
  2. Proliferation of daughter cells occurs, extracellular protein degradation enzymes - collagenases, elastases
    Basal lamina forms bud
  3. Epithelial cells invade space created
  4. Exocrine gland - central cells die off, canalicularisation
    Endocrine gland - angiogenic factors stimulate blood vessel growth in and around epithelial cells
  5. Link to mother cells broken through apoptosis
    Elongation factors extend gland if exocrine
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13
Q

Compare endocrine gland and follicular endocrine gland formation

A

From basal lamina bud that forms by proliferation
Endocrine produces angiogenic factors
Vascular endothelial growth factor, blood vessels around
In follicular expansion of cells but blood vessels circle around rather than intertwined
In thyroid follicles, production of colloid between epithelial cells causes expansion of follicle into sphere.

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14
Q

How does branching of epithelial cells occur?

A

Basic FG10 released by immature fibroblasts in mesenchyme
Epithelial cells move towards signal, towards duct
1. Tube elongation GF 1 active, 2 inactive
2. Tubule branching GF1 inactive, 2 active
Branching it splits into two.

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15
Q

Describe different simple duct structures and examples

A

Simple tubular - one single tube, intestinal glands
Simple branched tubular - 3 little tree tubes, gastric gland
Simple alveolar - one rounded branch, no example
Simple branched alveoli - like a clover, sebaceous glands

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16
Q

Describe different compound duct structures and examples

A

Compound tubular - many branches with long tubes, duodenal glands of small intestine
Compound alveolar - many clovers, mammary glands
Compound tubuloalveolar - lots of long tubes clovers ends. salivary glands

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17
Q

What are the two types of epithelial cells in exocrine glands?

A
  1. The cell lining the ducts
  2. The cells that make secretory products
    Some can turn into myoepithelial cells - features of epithelial and smooth muscle - squeeze the grapes!
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18
Q

Describe the structure of the salivary glands

A

Prebud forms initial bud to pseudoglandular.
Contains interlobilar and intercalated ducts between lobules. Joins acini to main duct. Contains striated ducts.
Serous demilune - half moon attached to another acinus.
Serous and mucous acinus. Myoepithelial cells around edge - squeeze.

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19
Q

What are the secretions of salivary glands?

A

3 types of mechanism and 2 types of secretion.
Serous only acinus produce only serum, mucous only produce mucus. Both those that pass through intercalated can produce watery mucus combination.

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20
Q

Describe the structure of the breast and mammary glands.

A

Same process as salivary gland development in utero.
Development then halts until puberty, prior to gender assignment in utero.
At puberty, oestrogen and progesterone produced by the ovaries restarts breast development.
During pregnancy, prolactin stimulates production of breast secretions colostrum.
Primary mammary bud extends into dermis towards mesenchyme.
Mammary pit and glands begin to form until production of lactiferous duct and site of depressed nipple.

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21
Q

What hormones allow breast development?

A

Oestrogen formation of terminal bud ends and allows ductal elongation.
Progestrone side branching and also ductal elongation.
Prolactin alveologenesis and lactogenic differentiation.

22
Q

What is merocrine secretion?

A

Use of secretory vesicle diffusing into surroundings.

23
Q

What is apocrine secretion?

A

Still forming of vesicles, but entire apical portion pinched off cell in secretion.

24
Q

What is holocrine secretion?

A

Mature cell dies and becomes secretory product, whole cell is released into duct or tissue.

25
Q

What is a merocrine gland?

A

Fusion of vesicles with apical membrane such as acinar and endocrine glands of the pancreas
Form of exocytosis

26
Q

What is an apocrine gland?

A

Partial loss of cytoplasm, lactating mammary gland or sweat glands in axilla and external genitalia

27
Q

What is a holocrine gland?

A

Complete loss of cytoplasm or cell such as sebaceous gland in skin and tarsal glands in eyelids

28
Q

What is a cytocrine gland?

A

Cells are released as a secretion such as spermatid in the seminiferous tube of testes

29
Q

What are the two pathways of exocytosis merocrine secretion?

A

Regulated and constitutive secretion

30
Q

What are the differences between regulated and constitutive secretion?

A

Regulated - secretory granules accumulating in large vesicles and released up stimulation. Need calcium
Constitutive - secretory product not converted into granules, packaged into small vesicles and continuously released to cells surface. No signal needed.
Mainly to repopulate the plasma membrane with proteins

31
Q

Describe merocrine secretion in greater detail.

A
  1. Contents of vesicle can be anything in the cell
  2. Active secretion requires specific signal
  3. Vesicle migrates to cell surface along microtubules
  4. Presence of calcium ions allows membrane of vesicles to fuse with plasmalemma, SNARE complex
  5. Cargo released to extracellular space
    Needs ATP
32
Q

Give a clinically relevant example of merocrine secretion.

A
  1. Food releases glucose into body
  2. Binds to GLUT-2 transporter on cell membrane
  3. ATP from glycolysis closes K channel so K concentration increases within the cell
  4. Membrane depolarisation opens calcium channels
  5. Calcium influx causes release of insulin
    Sulphonylurea receptors detect ATP levels and can close potassium channel to increase insulin release, used in Type 1 diabetes drugs.
33
Q

Give a clinically relevant example of apocrine secretion

A

Secretion from the breast.
During neonatal period only fats secreted by apocrine secretion.
Milk proteins made in RER and released by merocine.
During lactation fats and proteins build up into vesicles, lower half of cell becomes unstable breaks off by apocrine.

34
Q

Give a clinically relevant example of holocrine secretion

A

Sebaceous glands secretion
Secretory cell gradually fills up with secretory granules, makes more oil. Cell organelles degenerate, cell dies.
Plasma membrane breaks and secretum empties out.
Dead cells replaced by mitotic division of basal cells.
Become so large before they burst. Surrounded by thin layer of duct cells which do not produce sebum.

35
Q

What is the role of the golgi apparatus in secretion?

A

No control in constituative as not needed to modify proteins in any way.
In regulated - proteins can be glycosylated, stored in vesicles or sent to endosome, decide where it goes.

36
Q

Define the glycosylation of proteins.

A

The covalent attachment of sugars by enzymes to proteins and lipids to form glycoproteins and glycolipids.
Different to glyclation (non enzyme glycosylation)

37
Q

What are some roles of glycosylation?

A

To aid protein folding
Prevents protein and lipid digestion by intracellular enzymes
Cell recognition - in blood groups
Role on cell to extraceullar matrix attachment

38
Q

What is exocytosis and endocytosis?

A

Exocytosis - secretion of molecules outside the cell via a vesicle fusing to a membrane.
Endocytosis - engulfing of molecules inside the cell via vesicle formation.

39
Q

Define phagocytosis and pinocytosis.

A

Phagocytosis is the process by which cells envelop or engulf other cells.
Pinocytosis is the process by which lipid droplets are ingested by cells.

40
Q

What is receptor mediated endocytosis?

A

Receptors put on the surface of the cell known as clathrin, they pull in material from outside the cell and make coated vesicles. Way to transport drugs through tissues in circulation.

41
Q

What processes use phagocytosis and pinocytosis?

A

Phagocytosis used mainly by cells of immune system such as macrophages, dendritic cells, neutrophils.
Pinocytosis used especially by smooth muscle cells, do not receive signals from the environment so survey outside.

42
Q

What is transcytosis?

A

Transepithelial transport:

  • Paracellular transport - through aqueous channels
  • Transcellular transport - through lipid cell membranes
  • Aided by carrier proteins by counter-transport
  • Bind to cell surface receptors, endo/exocytosis
43
Q

What are some examples of transepithelial transport?

A

Amino acids for hormone production
Steroid hormones
Thyroxine transport across thyroid follicular cell
Cholesterol transport

44
Q

What are the types of glandular control?

A

Humoural stimulus, neural stimulus, hormonal stimulus

45
Q

Describe an example of humoral glandular control

A

Capillary blood contains low concentrations of calcium which stimulates PTH secretion - increases blood calcium.
Increases ostoclast action to mine bone and release.
Most prevalent in endocrine glands.

46
Q

Give an example of neural stimulus control

A

Preganglionic sympathetic fibres stimulate adrenal medulla cells, secretion of catecholamines.
Solely controls exocrine gland secretion - salivary.

47
Q

Give an example of hormonal stimulus control

A

Hypothalamus secretes hormones that stimulate anterior pituitary gland to secrete hormones that stimulate other endocrine glands and secretes hormones.
Mainly in endocrine glands.

48
Q

How are gland secretions controlled?

A

Primarily controlled by negative feedback mechanisms.
Hormonal - hypothalamus, pituitary, gland, target cells.
Neural - nervous system, endocrine gland, target
Humoral - substance level in plasma, gland, target

49
Q

What is an example of neurocrine communication?

A

The hypothalamus to the pituitary,

50
Q

What is the hypothalamo-hypophyseal portal system and how does it work?

A

Connects hypothalamus with anterior pituitary for quick transport and exchange. Capillaries pass into bloodstream, fenestrated for fast exchange.
Neurons in hypothalamus secrete hormones into capillaries, passes through infundibulum, to anterior pituitary, then release of secondary hormones.

Body Logistics (9 decks)

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